It is known practice to dye keratin fibers, such as human hair, with dye compositions containing oxidation dye precursors, which are generally known as oxidation bases. These oxidation bases can be colorless or weakly colored compounds, which, when combined with oxidizing products, may give rise to colored compounds by a process of oxidative condensation. It is also known that the shades obtained with these oxidation bases may be varied by combining them with couplers or coloration modifiers.
The variety of molecules that may used as oxidation bases and couplers allows a wide range of colors to be obtained.
The oxidation dyeing process can comprise applying to the keratin fibers at least one base or a mixture of bases and couplers with aqueous hydrogen peroxide solution as oxidizing agent, leaving the mixture to act, and then rinsing the fibers. This process, which is generally performed at basic pH, makes it possible simultaneously to obtain dyeing and lightening of the fiber that is reflected in practice by the possibility of obtaining a final coloration that is lighter than the original color.
This type of coloration should, moreover, satisfy a certain number of requirements. Thus, it should not have toxicological drawbacks, it may be able to produce shades in the desired intensity, and may show good resistance to external agents such as light, bad weather, washing, permanent-waving, perspiration and rubbing. The dyes may also be able to cover white hairs and they may be as unselective as possible, i.e., they may produce the smallest possible differences in coloration along the same keratin fiber, which may in fact be differently sensitized (damaged) between its end and its root. They may also show good chemical stability in formulations and have a good toxicological profile.
In the field of hair dyeing, para-phenylenediamine and para-tolylenediamine are oxidation bases that are widely used. They can make it possible with oxidation couplers to obtain varied shades.
However, there is a need in the art for new oxidation bases that have a better toxicological profile than para-phenylenediamine and para-tolylenediamine, while at the same time giving the hair at least one excellent property in terms of color intensity, variety of shades, color uniformity and resistance to external agents.